Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/12—Hydrolysis
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2800/00—Copolymer characterised by the proportions of the comonomers expressed
  • C08F2800/20—Copolymer characterised by the proportions of the comonomers expressed as weight or mass percentages
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2810/00—Chemical modification of a polymer
  • C08F2810/20—Chemical modification of a polymer leading to a crosslinking, either explicitly or inherently

Definitions

• the invention relates to a method for producing superabsorbent polymers based on finely divided, uncrosslinked and crosslinked aqueous polyacrylonitrile emulsions ,
• Superabsorbent polymers are known and are mainly used in Manufacture of diapers and incontinence articles, but also as water-storing Materials used in agriculture and for sheathing electrical cables. As a rule, it is the commercially available superabsorbent Polymers to widely cross-linked, water-insoluble polymers Base of alkali salts of polyacrylic acid or copolymers of acrylic acid and acrylamide, which are obtained by radical copolymerization of acrylic acid and polyfunctional monomers, e.g.
• Divinylbenzene, ethylene glycol dimethacrylate, Ethylene glycol diallyl ether, butanediol acrylate, hexanediol methacrylate, polyglycol diacrylate, Trimethylolpropane diacrylate, allyl acrylate, diallylacrylamide, triallylamine, Diallyl ether, methylenebisacrylamide and N-methylolacrylamide can be obtained. Due to their molecular structure, such polymers are able to Swelling and formation of hydrogels absorb large amounts of liquids and to hold them under pressure.
• EP-A-670 335 and EP-A-697 416 superabsorbents are used Polymers with extremely high swelling capacity and high gel strength described. These products are obtained by alkaline hydrolysis of polyacrylonitrile (PAN) emulsions at temperatures between 50-100 ° C and reaction times from 1 to 2 hours. In this process, products are added after hydrolysis superabsorbent properties due to precipitation with solvents, e.g. aliphatic monoalcohols, isolated as fine powder. After filtering and The superabsorbent polymers are dried to the desired grain size range ground.
• PAN polyacrylonitrile
• the finely divided, aqueous, high molecular weight, uncrosslinked or crosslinked polyacrylonitrile emulsions required for the production of the superabsorbent polymers are obtained by the homo- and / or copolymerization of acrylonitrile in the presence of special anionic polymeric emulsifiers (EP-A-590 460).
• the molecular weights of the uncrosslinked polyacrylonitrile emulsions prepared by this process are in the range from 5 ⁇ 10 5 to 1 ⁇ 10 7 g / mol, preferably from 2 ⁇ 10 6 to 5 ⁇ 10 6 g / mol.
• the particle sizes of the uncrosslinked or crosslinked aqueous PAN emulsions are in the range between 100 and 300 nm, preferably between 100 and 200 nm (determined by means of laser correlation spectroscopy).
• EP-A-783 005 is a process for continuous production described by superabsorbent polymers, in which aqueous Emulsions of crosslinked or uncrosslinked polyacrylonitrile homo- and / or Copolymers in one for the implementation of highly viscous reactions continuously working, mixing and kneading long-term reactor ("list reactor”) hydrolyzed by reaction with aqueous alkali hydroxide solutions at 70 to 100 ° C.
• the construction of the "list reactor” allows hydrolysis reactions on PAN emulsions perform in highly concentrated reaction mixtures. You can the concentrations of the crosslinked and uncrosslinked polyacrylonitrile emulsions in the reaction mixture during the hydrolysis amount to 10 to 40% by weight, so that as Consequence of the weight gain of the polymer caused by the hydrolysis approx. 60%, based on the polyacrylonitrile to be hydrolyzed, the final concentration in the reaction mixture is between 16 and 60% by weight.
• the invention relates to a method for producing superabsorbent Polymers in which uncrosslinked or crosslinked highly concentrated aqueous polyacrylonitrile emulsions by mixing with an alkali hydroxide solution and without further mixing under adiabatic reaction conditions ("as a block") be hydrolyzed.
• the starting temperature of the reaction mixture is generally 10 to 40 ° C, preferably 20 to 30 ° C. Because of the released Heat of reaction increases the temperature of the reaction mixture within 1.5 to 2.5 hours at 70 to 80 ° C. The rate of this temperature rise can on the one hand by a change in the initial temperature and by the layer thickness of the reaction mixture and on the other hand by changing the concentration and the stoichiometric ratios of the components in the starting reaction mixture to be controlled.
• the dwell time after reaching the maximum temperature is in Range from 0 to 6 hours, preferably 1 to 5 hours.
• the entire duration of the Hydrolysis is between 2 and 8 hours, preferably between 3 and 6 hours.
• the molar ratio of nitrile groups is in the starting polymers to the hydroxyl groups of the alkali metal hydroxides in the range from 1: 0.5 to 1: 1, preferred from 1: 0.6 to 1: 0.8.
• the final volume of the reaction mixture can change (Gels) due to the ammonia escaping during the hydrolysis Increase 10 to 30% by volume.
• the process according to the invention makes it possible to use reaction mixtures with a Solids concentration of more than 35 wt .-% produce.
• the further work-up of the elastic produced after the alkaline hydrolysis Gels to the desired powdery product with superabsorbent Properties can be applied using well-known process engineering Methods (e.g. analogous to EP-A 783 005 and EP-A 670 335) in particular Crushing the gel, neutralization, washing drying, grinding carried out become.
• the crushing of the elastic gel into gel particles with a particle size from 1 to 5 mm can be made in an extruder with a perforated plate become.
• the neutralization of the product can be done either in a water-alcohol mixture or by spraying with acid on the surface of the gel granulate respectively. This spraying process is followed by a water-alcohol mixture washed and the product isolated by filtration. After this Drying and grinding this filter residue to the desired grain size range
• the operational superabsorber is then available from 100 to 850 ⁇ m.
• the superabsorbent polymers obtainable in the manner described above have excellent application properties. This is how products, degrees of swelling made from uncrosslinked PAN emulsions between 380 and 700 g / g in deionized water and between 45 and 60 g / g in a 0.9% NaCl solution.
• the degrees of swelling are superabsorbers obtained in the following ranges: between 300 and 450 g / g in deionized water and between 30 and 47 g / g in 0.9% NaCl solution.
• the superabsorbent polymers according to the invention are, for example, in Hygiene products, such as baby diapers and incontinence articles, as water-storing Materials used in agriculture or in the sheathing of electrical cables.
• the subject of the registration are hygiene articles, water-storing materials in agriculture and sheaths of electrical cables made from the superabsorbent polymers according to the invention.
• a homogenized reaction mixture of 20.0 kg of this PAN emulsion and 7.332 kg of a 47% by weight aqueous NaOH solution is in a stirrer-free 60 1 reactor, at the bottom of which there is an opening, at 25 ° C. under nitrogen submitted.
• the layer thickness of the reaction mixture in the reactor is approximately 20 cm.
• the starting reaction mixture accordingly has the following composition: Concentration of polyacrylonitrile ([PAN]) 21.14% by weight Concentration of sodium hydroxide solution ([NaOH]) 12.61% by weight Molar ratio of PAN to NaOH 1: 0.79 Weight ratio of PAN to water 1: 3.13
• reaction mixture warms up adiabatically within 2 hours the heat of reaction released to a temperature of 79 ° C. After that it will Reaction mixture kept at this temperature in the reactor for a further 4 hours.
• the total residence time is 6 hours. After this reaction time there was a carboxyl group content of 75 mol% reached (determined by means of IR spectroscopy). After the reaction, a highly elastic gel block was created.
• the ammonia released which is approximately 15% by weight of the total amount of ammonia released, is removed from the reactor via a special outlet opening under a stream of N 2 and then absorbed by introduction into 20% sulfuric acid.
• the remaining 85% by weight of the amount of ammonia released remain in the gel block and are largely removed when the gel is crushed in the extruder under a stream of N 2.
• the remaining 20 to 23% by weight are in a water / alcohol mixture neutralized with acetic acid).
• the elastic gel in the form of a block is formed through the bottom opening pulled out ("The block to a certain extent falls out of the reactor by itself out”).
• the gel is then cut into smaller pieces and comminuted in an extruder with a perforated plate while simultaneously removing the ammonia under a stream of N 2 to a particle size in the range from 1 to 5 mm.
• the crushed, non-sticky gel granules obtained are used to carry out the Neutralization divided into three equal portions.
• the first serving is in neutralized a water-ethanol mixture with 20% acetic acid. Here is the volume ratio of ethanol to water in the mixture 1: 1 to 1: 1.2.
• To The product is filtered off and washed at temperatures between 70 and 80 ° C dried. Subsequently, the dried product is on a particle size spectrum ground down from 100 to 850 ⁇ m.
• 250 mg of the superabsorbent polymer to be investigated are placed in a 300 Weighed ml-beaker and with 250 to 300 ml of distilled water or with 50 Pour ml of a 0.9% by weight NaCl solution and leave to stand.
• the gel obtained is over filter a filter cloth with a mesh size of 30 ⁇ m or a paper filter and balanced.
• the degree of swelling is then calculated from the ratio of the weight to weight in g / g. Each determination is carried out three times. The measurement accuracy is about 5%.
• the degree of swelling of the product produced according to Example 1 is 630 g / g in distilled water and 57.5 g / g in 0.9% NaCl solution.
• the pH of the product obtained according to Example 1 is 0.9% in NaCl solution 6.5.
• the neutralization procedures for the products were changed as well as the Hydrolysis conditions (the PAN concentration in the reaction mixture, the PAN emulsion type, the molar ratio of PAN to NaOH, the weight ratio of PAN to water, residence time and start temperature for hydrolysis) varies.
• Example 1 That according to Example 1 after comminution in the form of gel-like particles with a size between 1 and 4 mm of product (second portion) was obtained Spray neutralized with 20% acetic acid. After that it was Product in an ethanol-water mixture with a volume ratio of ethanol washed to 1: 1 water and filtered. After drying, the product ground to a particle size spectrum of 100 to 850 microns.
• the comminuted gel granules obtained according to Example 1 were at a temperature of 80 ° C without neutralization up to a residual moisture of approx. 15% by weight dried.
• a large part of the ammonia split off removed, and only about 3 to 4 wt .-% remain in the dried product, the be neutralized by acetic acid in the subsequent neutralization process.
• the neutralization of the dried product with the particle size range of 0.3 to 2 mm was in an ethanol-water mixture (volume ratio of Ethanol to water 1: 1) with 20% acetic acid.
• the product was filtered with an ethanol-water mixture washed and dried at a temperature between 70 and 80 ° C. After drying, the product was ground in such a way that a particle size distribution was obtained from 100 to 850 microns.
• the finished product obtained according to Example 2 with a particle size distribution of 100 to 850 ⁇ m was at a temperature of 180 ° C for about 15 minutes in a forced air drying cabinet heated
• the measured high degrees of swelling clearly show the excellent ones application properties of the adiabatic hydrolysis obtained superabsorbent.
• a hydrolysis was carried out by incorporating 0.75% by weight of divinylbenzene weakly crosslinked polyacrylonitrile emulsion with an average particle size of 118 nm and a solids content of 24.2%.
• Table 1 shows the reaction conditions and the performance properties of the product obtained.
• the superabsorbent polymers prepared according to Examples 1 to 7 were additionally subjected to surface modification with formaldehyde and silica.
• surface modification 35 g of the superabsorbent polymers obtained according to Examples 1 to 7 are stirred for 20 minutes at room temperature with 200 g of a reaction mixture of the following composition: 178,0g methanol 18.0 g deionized water 3.0 g silica 1.0 g formaldehyde
• the crude product After filtration through a suction filter, the crude product has a solids content of 70.1% by weight for 30 minutes at 98 ° C. in a circulating air cabinet.
• Table 2 also shows the water-soluble components (WLA) and the pH values of the superabsorbent polymers prepared according to Examples 1 to 7 compiled. All investigations were carried out with 0.9% NaCl solution.

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• Chemical & Material Sciences (AREA)
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• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
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Citations (7)

• 2000
  • 2000-11-30 DE DE10059593A patent/DE10059593A1/de not_active Withdrawn
• 2001
  • 2001-11-19 EP EP01127301A patent/EP1211266A1/fr not_active Withdrawn
  • 2001-11-21 JP JP2001355773A patent/JP2002201214A/ja active Pending
  • 2001-11-27 US US09/995,330 patent/US20020128396A1/en not_active Abandoned
  • 2001-11-28 TW TW090129359A patent/TW538062B/zh not_active IP Right Cessation

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